Dustin Johnson surged into the halfway lead as world No 1 Justin Rose suffered a rare missed cut in the inaugural Saudi International.
Johnson carded an eagle and seven birdies to set a new course record of 61 at Royal Greens Golf & Country Club, eclipsing the mark of 63 established by Belgium's Thomas Pieters on day one of the £2.6million event.
That left the world No 3 with a three-shot lead over China's Li Haotong and South African Zander Lombard, with Paraguay's Fabrizio Zanotti and Australia's Scott Hend a shot further back.
Rose came into the week on the back of winning his 10th PGA Tour title in the Farmers Insurance Open, but a double bogey on the 16th proved costly as a second round of 72 meant the 38-year-old missed just his second cut since August 2017, a total of 36 events.
"The mistakes I made I felt were due to trying to chase the cut and that doesn't happen if I had putted a bit better the first day," said Rose, whose last early exit from a regular European Tour event was in Hong Kong in December 2011.
"I actually played really nicely day one. Today I felt not as good, but I think the mistakes were more because I was behind the eight-ball trying to get into the tournament."
Johnson, who started his round from the 10th, had an outside chance of recording the second 59 in European Tour history when he went to the turn in 31 and picked up further birdies on the second, sixth and seventh, as well as eagle from 25 feet on the fourth.
However, the former US Open champion had to settle for pars on his last two holes and admitted he was not even thinking about joining England's Oliver Fisher in the history books.
"I mean, I was trying to go birdie-birdie, but I never really thought about it," Johnson told Sky Sports. "I wasn't even thinking it was a par-70. I was just trying to keep getting my score lower and lower.
"It was really good. Obviously you always have fun when you're playing well, but I did a lot of the same things I did yesterday. The greens rolled a little bit better today.
"I felt like I paid a lot more attention to exactly what the putts were going to do and just kind of tried to make sure I just trusted the line that I was playing and made some putts today. You know, I drove it really well and gave myself a lot of opportunities."
Li was penalised two shots on the final hole of the Dubai Desert Classic last week because his caddie was on a direct line behind the ball when he began to take his stance on the green.
That was in breach of rule 10.2b(4), one of a number amended at the start of
2019, and meant the defending champion dropped from a tie for third to a tie for 12th, costing him more than 80,000 euros.
Controversy over the ruling prompted European Tour chief executive Keith Pelley to contact the R&A to voice his displeasure at what he called a "grossly unfair" penalty, but Li was keen to move on following a second round of 65.
"It is very pleasing," Li said. "I was disappointed in number four, which is a birdie hole and became a bogey, which is a two-shot (swing) there. But I think everything I did very well."
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